Multilayer pillar for reduced stress interconnect and method of making same

ABSTRACT

A multi-layer pillar and method of fabricating the same is provided. The multi-layer pillar is used as an interconnect between a chip and substrate. The pillar has at least one low strength, high ductility deformation region configured to absorb force imposed during chip assembly and thermal excursions.

FIELD OF THE INVENTION

The present invention relates generally to a multi-layer pillar andmethod of fabricating the same and, more particularly, to a multi-layerpillar interconnect and method of fabricating the same.

BACKGROUND OF THE INVENTION

Traditionally, high temperature C4 (Controlled Collapse Chip Connection)bumps have been used to bond a chip to a substrate. Conventionally, theC4 bumps are made from leaded solder, as it has superior properties. Forexample, the lead is known to mitigate thermal coefficient (TCE)mismatch between the package and the substrate. Accordingly, stressesimposed during the cooling cycle are mitigated by the C4 bumps, thuspreventing delaminations or other damage from occurring to the chip orthe substrate.

However, lead-free requirements imposed by the European Union ontoelectronic components are forcing manufacturers to implement new ways toproduce chip-to-substrate-joints. For example, manufactures have usedsolder interconnects consisting of copper as a replacement for leadedsolder interconnents. More specifically, another type of lead freechip-to-substrate-connection is copper pillar technology. In suchjoints, a solder C4 bump is replaced with a copper pillar or copperpillars plated onto a chip's Under Bump Metallization (UBM). Suchconnection allows plating of long (80-100 um), small diameter (30-60 um)copper pillars. Also, such chip to package connections are favorablesince they offer higher connection density, superior electricalconductivity and allows more uniform current distribution and heatdissipating performance, and hence potentially increased reliability.

However, copper has a high Young's modulus and a high thermal expansion.This being the case, copper is not an ideal candidate for mitigatingthermal coefficient (TCE) mismatch between the chip and the substrate.Accordingly, stresses imposed during the cooling cycle cannot beeffectively mitigated by the copper pillars, thus resulting in fracturesor delaminations or other damage to the package.

Accordingly, there exists a need in the art to overcome the deficienciesand limitations described hereinabove.

SUMMARY OF THE INVENTION

In a first aspect of the invention a structure comprises a modulatedcopper pillar having at least one low strength, high ductilitydeformation region configured to absorb force imposed during chipassembly and thermal excursions.

In another aspect of the invention, an interconnect pillar comprises anintermediate layer interposed between two copper layers. Theintermediate layer has a lower modulus of elasticity than that of thetwo copper layers and thereby is configured to absorb stress imposedduring a cooling cycle of an interconnect process which would otherwisebe imparted onto a chip.

In another aspect of the invention, a method of forming a structurecomprises forming a first copper layer; interrupting the forming of thefirst copper layer to form an intermediate layer; and forming a secondcopper layer on the intermediate layer. The intermediate layer has amodulus of elasticity lower than the first copper layer and the secondcopper layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention,in which:

FIG. 1 shows a first implementation of a multi-layer copper pillar inaccordance with the invention;

FIG. 2 shows a second implementation of a multi-layer copper pillar inaccordance with the invention;

FIG. 3 shows a third implementation of a multi-layer copper pillar inaccordance with the invention;

FIG. 4 shows a fourth implementation of a multi-layer copper pillar inaccordance with the invention; and

FIG. 5 shows a structure implementing the multi-layer copper pillar inaccordance with the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention relates generally to a multi-layer pillarinterconnect and method of fabricating the multi-layer pillarinterconnect and, more particularly, to a multi-layer pillar configuredand structured to reduce stress at the joint between the pillar and achip. In embodiments, copper pillar technology is improved by theaddition of one or more layers of high ductility and low strength metalas intermediate layers. The metals, in embodiments, have a higherductility and lower Young's modulus than copper. The addition of one ormore layers of metal creates low strength, high ductility “deformation”or stress relieving regions which absorb tensile stresses generatedduring chip assembly (reflow) processes, e.g., during the cooling cycleof the chip-substrate joining process.

In one mechanism, the intermediate metal layers allow the pillar to tiltand/or slide to compensate for Thermal Coefficient of Expansion (TCE)mismatch between the chip and the substrate (e.g., organic laminate).This may be due to the melting of the material during the heatingprocesses (e.g., peak temperature being about 240° C. to 270° C.). Inanother mechanism, the intermediate metal layers, being more ductilethan copper, can absorb stresses created during the cooling cycle (whichwould otherwise be imparted onto the chip or copper metallurgy, itself).Thus, by implementing the structures of the invention, stresses normallytransmitted to the chip will be absorbed by the intermediate metallayers in the structures of the invention, preventing chip damage andincreasing module yield.

First Embodiment of the Invention

In the embodiment of FIG. 1, a multi-layer pillar in accordance with theinvention is generally depicted as reference numeral 10. In embodiments,the multi-layer pillar 10 is typically between 60 to 80 microns inthickness; although any thickness for a particular application iscontemplated by the invention. Accordingly, the invention should not belimited to the exemplary illustration of between 60 to 80 microns inthickness, in any of the embodiments.

The multi-layer pillar 10 includes a barrier and adhesion layer 12. Inone embodiment, the barrier and adhesion layer 12 may be TitaniumTungsten (TiW); although, other barrier and adhesion materials are alsocontemplated by the invention. For example, as should be understood bythose of skill in the art, the barrier and adhesion layer 12 can be anymaterial which prevents diffusion of materials between a chip (shown inFIG. 5) and materials of the multi-layer pillar 10 or substrate (shownin FIG. 5).

Still referring to FIG. 1, a seed layer 14 is formed on the barrier andadhesion layer 12. In embodiments, the seed layer 14 is Chromium Copper(Cr/Cu). Alternatively, the seed layer 14 is Copper (Cu). The seed layer14 may be formed by any conventional chemical or physical vapordeposition process (CVD or PVD). As should be understood by those ofskill in the art, the seed layer 14 is used for the formation of thecopper layer of the pillar, in subsequent processing steps.

A copper layer 16 a is formed on the seed layer 14 to a certain height,depending on the particular application. In embodiments, the copper 16 ais formed in a high-deposition-rate electroplating bath. At apredetermined time and/or height of the copper column the electroplatingof copper is interrupted in order to form a low strength, high ductilelayer 18 a (e.g., solder-type disc layer) on the copper layer 16 a. Inembodiments, the formation of the copper column can be interrupted whenthe copper column is about 5 to 30 um. The low strength, high ductilelayer 18 a is an intermediate layer of about 5 to 20 microns and morepreferably 5 to 10 microns, formed by a deposition process. Thedeposition process may be provided by an electrolytic bath, inembodiments.

In embodiments, the low strength, high ductile layer 18 a is, forexample, Tin (Sn), Bismuth (Bi) or Indium (In), depending on theparticular application. The Young's modulus (modulus of elasticity) ofSn is 50, the Young's modulus of Bi is 32 and the Young's modulus of Inis 11; whereas, the Young's modulus of Cu is 130. Moreover, the rigiditymodulus (i.e., the change of shape produced by a tangential stress) ofSn is 18, the rigidity modulus of Bi 12 and the rigidity modulus of Inis 12; whereas the rigidity modulus of Cu is 48.

According to the principles of the invention, as the materials of layer18 a are less rigid (of lower strength) than copper, once formed, theentire pillar is capable of sliding or tilting to compensate for ThermalCoefficient of Expansion (TCE) mismatch between the chip and thesubstrate (e.g., organic laminate) during heating processes. This may bedue to the melting of the material during the chip-joining processes(e.g., peak temperature being about 240° C. to 270° C.). In anothermechanism, as the materials used for the layer 18 a are more ductilethan copper, such materials can absorb stresses created during thecooling cycle. That is, the low strength, high ductile layer 18 a formsa low strength, high ductile region which absorbs forces imposed duringthe chip assembly and thermal excursions of the interconnect processthereby absorbing stresses that would otherwise have been transmitted tothe chip or copper metallurgy. Thus, by implementing the structures ofthe invention, stresses normally imposed on the chip or coppermetallurgy will be absorbed by layer 18 a in the structures of theinvention, preventing chip damage, delamination of UBM structure andincreasing module yield.

In embodiments, an optional nickel barrier layer 20 (at the interfacebetween the low strength, high ductile layer 18 a and the copperlayer(s)) can be used to minimize the interaction between high ductilelayer 18 a and the copper layer(s). In the case that the layer 18 a isSn, the reaction product between copper and tin, a material of higherelectrical resistivity, is relatively thicker. In the presence of theoptional nickel layer, this reaction product, a material of higherelectrical resistivity, between layer 18 a and the nickel layer isrelatively thinner. In embodiments, the optional nickel barrier layer 20is approximately 1.0 to 2.0 um in thickness. In further embodiments, theoptional nickel barrier layer 20 can be formed on both sides of the lowstrength, high ductile layer 18 a to prevent a reaction between thelayer 18 a (e.g., solder-type disc layer) and the copper.

A copper layer 16 b is formed on the low strength, high ductile layer 18a (or nickel layer 20) to form the remaining portions of the multi-layerpillar 10. Much like the copper layer 16 a, a high-rate electroplatingbath forms the copper layer 16 b. In further embodiments, the tip of themulti-layer pillar 10 can be plated with an optional solder disc 22 toprovide a connection to a substrate (FIG. 5) during a reflow process.

Second Embodiment of the Invention

In the embodiment of FIG. 2, the multi-layer pillar is generallydepicted as reference numeral 10. As in the embodiment of FIG. 1, themulti-layer pillar 10 is typically between 60 to 80 microns inthickness; although any thickness for a particular application iscontemplated by the invention. As discussed below, the embodiment ofFIG. 2 includes two or more intermediate layers.

The multi-layer pillar 10 includes a barrier and adhesion layer 12. Inone embodiment, the barrier and adhesion layer 12 may be TitaniumTungsten (TiW); although, other barrier and adhesion materials are alsocontemplated by the invention. Again, the barrier and adhesion layer 12can be any material which prevents diffusion of materials between a chip(shown in FIG. 5) and materials of the pillar 10 or substrate (shown inFIG. 5).

Still referring to FIG. 2, a seed layer 14 is formed on the barrier andadhesion layer 12. In embodiments, the seed layer 14 is Chromium Copper(Cr/Cu) or Copper (Cu). The seed layer 14 may be formed by anyconventional chemical or physical vapor deposition process (CVD or PVD).A copper layer 16 a is formed on the seed layer 14 to a certain height,depending on the particular application. In embodiments, the copperlayer 16 a is formed in a high-rate electroplating bath. In embodiments,the formation of the copper layer 16 a can be interrupted when thecopper column is about 5 to 30 um.

As discussed above, prior to the formation of the entire pillar 10, theelectroplating of copper is interrupted in order to form a low strength,high ductile layer 18 a (e.g., solder-type disc layer) on the copperlayer 16 a. In embodiments, the high ductile metal 18 a is anintermediate layer of about 5 to 20 microns and more preferably 5 to 10microns, formed by a deposition process. The deposition process may beprovided by an electrolytic bath, in embodiments. In embodiments, thehigh ductile metal layer 18 a is, for example, Tin (Sn), Bismuth (Bi) orIndium (In), depending on the particular application.

In embodiments, an optional nickel barrier layer 20 (represented as theinterface between the low strength, high ductile layer 18 a and thecopper layer(s)) can be used to prevent the interaction between highductile layer 18 a and the copper layer(s). In the case that layer 18 ais Sn, the reaction product between copper and tin, a material of higherelectrical resistivity, is relatively thicker. In presence of theoptional nickel layer, this reaction product, a material of higherelectrical resistivity, between layer 18 a and the nickel layer isrelatively thinner minimize the interaction between high ductile layer18 a and the copper layer(s). In embodiments, the optional nickelbarrier layer is approximately 1.0 to 2.0 um in thickness. In furtherembodiments, the optional nickel barrier layer 20 can be formed on bothsides of the intermediate layer or layers to prevent a reaction betweenthe intermediate layers (e.g., solder-type disc layer) and the copper.

A second copper layer 16 b is formed on the low strength, high ductilelayer 18 a (or nickel layer) to form an additional portion of themulti-layer pillar 10. As with the copper layer 16 a, the copper layer16 b can be formed in a high-rate electroplating bath. Theelectroplating of copper is interrupted again to form a second lowstrength, high ductile layer 18 b (e.g., solder-type disc layer) on thecopper layer 16 b. In embodiments, the formation of the copper layer 16b can be interrupted when the copper column is about 10 to 30 um.

In embodiments, the low strength, high ductile layer 18 b is anintermediate layer of about 5 to 20 microns and more preferably 5 to 10microns, formed by a deposition process. The deposition process may beprovided by an electrolytic bath, in embodiments. In embodiments, thelow strength, high ductile layer 18 b is, for example, Tin (Sn), Bismuth(Bi) or Indium (In), depending on the particular application.

Again, according to the principles of the invention, as the materials oflayers 18 a, 18 b are less rigid (of lower strength) than copper, onceformed, the entire pillar is capable of sliding or tilting to compensatefor Thermal Coefficient of Expansion (during heating processes) mismatchbetween the chip and the substrate (e.g., organic laminate). In anothermechanism, as the materials used for the layers 18 a, 18 b are moreductile than copper, such materials can absorb stresses created duringthe cooling cycle. That is, the layers 18 a, 18 b form a low strength,high ductile region which absorb forces imposed during the chip assemblyand thermal excursions thereby absorbing stresses that would otherwisehave been transmitted to the chip or copper metallurgy. Thus, byimplementing the structures of the invention, stresses normallytransmitted to the chip or copper metallurgy will be absorbed by thelayers 18 a, 18 b in the structures of the invention, thereby preventingdelamination of the UBM layers.

A copper layer 16 c is formed on the low strength, high ductile layer 18b (or nickel layer) to form the remaining portion of the multi-layerpillar 10. As with the copper layers 16 a and 16 b, the copper layer 16c can be formed in a high-rate electroplating bath. In embodiments, theformation of the copper layer 16 c can be interrupted when the coppercolumn is about 20 to 30 um. Additionally, an optional nickel layer 20may be formed at the interfaces between the low strength, high ductilelayer 18 b and the copper layers 16 b, 16 c to prevent a reactionbetween the intermediate layer 18 b (e.g., solder-type disc layer) andthe copper layers 16 b, 16 c. In an optional embodiment, the tip of themulti-layer pillar 10 can be plated with an optional solder disc 22 toprovide a connection to a substrate (FIG. 5) during a reflow process.

In the embodiments of FIGS. 1 and 2, the number, position and thicknessof the low strength, high ductile layers can vary according totechnology application and space (e.g. chip size, number of C4 typeconnections, position of C4 connections on the chip, etc.).Additionally, the above materials for the low strength, high ductilelayers can vary depending on the technology, noting that the modulus ofelasticity should be lower than that of copper. Also, the number ofmodulated pillars in accordance with the invention deposited onto asingle Under Bump Metallization (UBM) may vary depending on theparticular application.

Third Embodiment of the Invention

FIG. 3 shows a third embodiment in accordance with the invention. Inthis embodiment, the multi-layer pillar 10 includes high melting pointmaterials as discussed below. In embodiments, the multi-layer pillar 10is typically between 60 to 80 microns in thickness; although anythickness for a particular application is contemplated by the invention.

The multi-layer pillar 10 includes a barrier and adhesion layer 12. Inone embodiment, the barrier and adhesion layer 12 may be TitaniumTungsten (TiW); although, other barrier and adhesion materials arecontemplated by the invention. A seed layer 14 is formed on the barrierand adhesion layer 12. In embodiments, the seed layer 14 is ChromiumCopper (Cr/Cu) or Copper (Cu). The seed layer 14 may be formed by anyconventional chemical deposition or physical deposition (CVD or PVD)method.

A copper layer 16 a is formed on the seed layer 14 to a certain height,depending on the particular application. In embodiments, the formationof the copper layer 16 a can be interrupted when the copper column isabout 5 to 30 um. In embodiments, the copper layer 16 a is formed in ahigh-rate electroplating bath. The electroplating of copper isinterrupted to form a low strength, high ductile layer 18 a on thecopper layer 16 a. In embodiments, the low strength, high ductile layer18 a is an intermediate layer of about 0.2 to 2.0 micron, formed by adeposition process. The deposition process may be provided by anelectrolytic bath, in embodiments.

In embodiments, the low strength, high ductile layer 18 a is, forexample, Gold (Au), Silver (Ag) or Aluminum (Al), depending on theparticular application. The Young's modulus (modulus of elasticity) ofAu is 78, the Young's modulus of Ag is 83 and the Young's modulus of Alis 76; whereas, the Young's modulus of Cu is 130. Moreover, the rigiditymodulus (i.e., the change of shape produced by a tangential stress) ofAu is 27, the rigidity modulus of Ag 30 and the rigidity modulus of Alis 26; whereas the rigidity modulus of Cu is 48.

In the embodiment of FIG. 3, the low strength, high ductile layer 18 ahas a higher melting temperature than lead-free solder and, as such, itdoes not melt during the assembly processing. And, again, according tothe principles of the invention, the materials of low strength, highductile layer 18 a are configured such that the entire pillar is capableof sliding or tilting to compensate for Thermal Coefficient of Expansion(TCE) mismatch between the chip and the substrate (e.g., organiclaminate) during the cooling part of the chip joining processes. Inanother mechanism, the materials used for the low strength, high ductilelayer 18 a are more ductile than copper and, as such, are capable ofabsorbing stresses created during the cooling cycle. That is, the lowstrength, high ductile layer 18 a can deform during the cooling cyclethereby absorbing stresses that would otherwise have been imposed on theUBM metallurgy. Thus, by implementing the structures of the invention,stresses normally transmitted to the chip or copper metallurgy will beabsorbed by the low strength, high ductile layer in the structures ofthe invention, preventing delamination of UBM layers, chip damage andincreasing module yield.

In embodiments, an optional nickel barrier layer 20 can be formed onboth sides of the low strength, high ductile layer 18 a to have areduced reaction product between layer 18 a and prevent a reactionbetween the layer 18 a and the copper. A copper layer 16 b is formed onthe low strength, high ductile layer 18 a (or nickel layer 20) to formthe remaining portion of the multi-layer pillar 10. Much like the copperlayer 16 a, a high-rate electroplating process forms the copper layer 16b. In further embodiments, the tip of the multi-layer pillar 10 can beplated with an optional solder disc 22 to provide a connection to asubstrate (FIG. 5) during a reflow process.

Fourth Embodiment of the Invention

In the embodiment of FIG. 4, the multi-layer pillar 10 includes two (ormore) intermediate layers, as discussed below. As in the embodiment ofFIGS. 1-3, the multi-layer pillar 10 is typically between 60 to 80microns in thickness; although any thickness for a particularapplication is contemplated by the invention.

The multi-layer pillar 10 includes a barrier and adhesion layer 12. Inone embodiment, the barrier and adhesion layer 12 may be TitaniumTungsten (TiW); although, other barrier and adhesion materials are alsocontemplated by the invention. Again, the barrier and adhesion layer 12can be any material which prevents diffusion of materials between a chip(shown in FIG. 5) and materials of the pillar 10 or substrate (shown inFIG. 5).

Still referring to FIG. 4, a seed layer 14 is formed on the barrier andadhesion layer 12. In embodiments, the seed layer 14 is Chromium Copper(Cr/Cu) or Copper (Cu). The seed layer 14 may be formed by anyconventional chemical or physical process (CVD or PVD). A copper layer16 a is formed on the seed layer 14 to a certain height, depending onthe particular application. In embodiments, the copper 16 a is formed ina high-rate electroplating bath.

Again, prior to the formation of the entire multi-layer pillar 10, theelectroplating of copper is interrupted in order to form a low strength,high ductile layer 18 a on the copper layer 16 a. In embodiments, theformation of the copper layer 16 a can be interrupted when the coppercolumn is about 5 to 30 um. In embodiments, the low strength, highductile layer 18 a is, for example, Gold (Au), Silver (Ag) or aluminum(Al), depending on the particular application. In embodiments, the lowstrength, high ductile layer 18 a is an intermediate layer of about 0.2to 2.0 micron, formed by a deposition process. The deposition processmay be provided in an electrolytic bath, in embodiments.

In embodiments, an optional nickel barrier layer 20 (at the interfacebetween the intermediate layer 18 a and the copper layer(s)) can beformed on both sides of the intermediate layer or layers to prevent areaction between the intermediate layers and the copper. A second copperlayer 16 b is formed on the low strength, high ductile layer 18 a (ornickel layer) to form an additional portion of the multi-layer pillar10. As with the layer 16 a, the copper layer 16 b can be formed in ahigh-rate electroplating bath. In embodiments, the formation of thecopper layer 16 b can be interrupted when the copper column is about 10to 30 um.

In embodiments, the electroplating of copper is interrupted to form asecond low strength, high ductile layer 18 b on the copper layer 16 b.In embodiments, the second high ductile metal layer 18 b is, forexample, Gold (Au), Silver (Ag) or aluminum (Al), depending on theparticular application. In embodiments, the second high ductile metallayer 18 b is an intermediate layer of about 0.2 to 2.0 micron, formedby a deposition process. The deposition process may be provided in anelectrolytic bath, in embodiments.

A copper layer 16 c is formed on the second high ductile metal layer 18b (or nickel layer) to form the remaining portion of the multi-layerpillar 10. As with the layers 16 a and 16 b, the copper layer 16 c canbe formed in a high-rate-electroplating bath. Additionally, an optionalnickel layer may be formed at the interfaces between the intermediatelayer 18 b and the copper layers 16 b, 16 c to prevent a reactionbetween the intermediate layer 18 b and the copper layers 16 b, 16 c. Inan optional embodiment, the tip of the multi-layer pillar 10 can beplated with an optional solder disc to provide a connection to asubstrate (FIG. 5) during a reflow process.

In the embodiment of FIG. 4, the layers 18 a, 18 b have a higher meltingtemperature than lead-free solder, and, as such do not melt duringassembly processing. Additionally, according to the principles of theinvention, the materials of layers 18 a, 18 b permit the entire pillarto slide or tilt to compensate for Thermal Coefficient of Expansion(TCE) mismatch between the chip and the substrate (e.g., organiclaminate) during the heating processes. In another mechanism, the layers18 a, 18 b are more ductile than copper and, as such, are capable ofabsorbing stresses created during the cooling cycle. That is, the layers18 a, 18 b can deform during the cooling cycle thereby absorbingstresses that would otherwise have been imposed on the UBM metallurgy.Thus, by implementing the structures of the invention, stresses normallytransmitted to the chip or copper metallurgy will be absorbed by layers18 a, 18 b in the structures of the invention, thereby preventing UBMfatigue and increasing module yield.

In the embodiments of FIGS. 3 and 4, the number, position and thicknessof the intermediate layers can vary according to technology applicationand space (e.g. chip size, number of C4 type connections, position of C4connections on the chip, etc.). Additionally, the above materials forthe intermediate layers can vary depending on the technology, notingthat the modulus of elasticity should be lower than that of copper.Also, the number of modulated pillars in accordance with the inventionthe deposited onto a single UBM may vary depending on the particularapplication.

Structure of the Invention

FIG. 5 shows a packaged structure in accordance with the invention. Inparticular, FIG. 5 shows the utilization of the multi-layer pillar 10 ofFIG. 1 bonded to a substrate 50 and a chip 60. It should be recognizedthat any of the structures discussed above can be implemented with thesubstrate 50 and chip 60 shown in FIG. 5.

In the structure of FIG. 5, a via 70 is provided in the substrate. Thevia 70 includes Cu and materials such as, for example, SnCu solder orSnCuAg solder or NiP and Au or Ag, to name a few materials, which can beused to assist in the bonding of the substrate 50 to the multi-layerpillar 10 during the heating process. That is, the material on the via70 will flow during the heating process, bonding the substrate 50 to themulti-layer pillar 10 or the solder on the copper pillar (disc 22 inFIG. 5) will flow and provide the bonding.

As should be understood by those of skill in the art, the chip 60 has alower CTE than that of the organic substrate 50. Thus, during thecooling cycle, the substrate 50 will shrink faster than the chip 50.Compared to a conventional structure, as the multi-layer pillar 10 ofthe invention includes a deformation zone, the stresses created by thesubstrate 50 (shrinking faster than chip 60) will be absorbed by themulti-layer pillar 10. This will protect the chip from fracture oflayers under the UBM during the connection process and thermalexcursions thus increasing overall module yield and reliability.

The methods and structures as described above are used in thefabrication of integrated circuit chips. The resulting integratedcircuit chips can be distributed by the fabricator in raw wafer form(that is, as a single wafer that has multiple unpackaged chips), as abare die, or in a packaged form. In the latter case the chip is mountedin a single chip package (such as a plastic carrier, with the structuresof the invention) or in a multichip package (such as a ceramic carrierthat has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While the invention has been described in terms of embodiments, thoseskilled in the art will recognize that the invention can be practicedwith modifications and in the spirit and scope of the appended claims.

What is claimed is:
 1. A method, comprising: providing a chip having abarrier and adhesion layer; forming a seed layer on the barrier andadhesion layer; forming a first copper layer on the seed layer; forminga first intermediate layer on the first copper layer; forming a secondcopper layer on first intermediate layer; forming a second intermediatelayer in direct contact with the second copper layer; forming a thirdcopper layer in direct contact with the second intermediate layer; andforming a first barrier protective layer at an interface between thefirst copper layer and the first intermediate layer, wherein the barrierand adhesion layer is Titanium Tungsten and the first barrier protectivelayer is nickel.
 2. The method of claim 1, further comprising forming acap layer on the third copper layer.
 3. The method of claim 2, whereinthe cap layer is solder.
 4. The method of claim 1, wherein the firstintermediate layer material is a single chemical element selected from agroup consisting of: gold, silver and aluminum.
 5. The method of claim1, further comprising: forming a second barrier protective layer at aninterface between the first intermediate layer and the second copperlayer.
 6. The method of claim 5, wherein each of the first and secondbarrier protective layers is nickel.
 7. The method of claim 1, whereinthe first, second, and third copper layers and the first and secondintermediate layers form a pillar that has an overall height which ismore than its width.
 8. The method of claim 1, wherein: the forming thefirst copper layer comprises electroplating the first copper layer onthe seed layer; and the forming the second copper layer comprises usingan electroplating bath to form the second copper layer.
 9. The method ofclaim 1, further comprising forming a third barrier protective layer atan interface between the first intermediate layer and the second copperlayer.
 10. The method of claim 1, further comprising providing no morethan three copper layers.
 11. The method of claim 10, further comprisingproviding no more than two intermediate layers.
 12. The method of claim11, wherein the first copper layer includes only copper.
 13. A method,comprising: providing a chip having a barrier and adhesion layer;forming a seed layer directly on the barrier and adhesion layer; forminga first copper layer on the seed layer; forming a first intermediatelayer directly on the first copper layer; forming a second copper layeron first intermediate layer; forming a second intermediate layer indirect contact with the second copper layer; forming a third copperlayer in direct contact with the second intermediate layer; and forminga barrier protective layer at an interface between the firstintermediate layer and the second copper layer, wherein the barrier andadhesion layer is Titanium Tungsten and the barrier protective layer isnickel.